U.S. Deportment of Transportation National Highway Traffic Safety Administration

8/14/2019 U.S. Deportment of Transportation National Highway Traffic Safety Administration

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U.S. Deportmentof TransportationNational HighwayTraffic SafetyAdministration

DOT HS 807 725

Final ReportMay 1991

Commercial Motor VehicleSpeed Control Devices

Prepared in Response toSection 9108; Public Law 100-690

Truck and Bus Safety and Regulatory Reform Act of 1988November 18, 1988

This document is available to the public from the National Technical Information Service, Springfield, Virginia 22161.


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Technical Report Documentation Page

1 . R e p o r t N o .

DOT HS 807 725

2 . G o v e r n m e n t A c c e s s i o n N o .

I

4. T i t l e a n d S u b t i t l e

Commercial Motor Vehicle Speed Control Safety

7 . A u t h o r s )

9 . P e r f o r m i n g O rg a n i z a t i o n N a m e a n d A d d r e s s

National Highway Traffic Safety AdministrationU.S. Department of Transportation400 Seventh Street, SW.Washington, DC 20590

1 2 . S p o n s o r i n g A g e n c y N a m e a n d Address

National Highway Traffic Safety Administration400 Seventh Street, SW.Washington, DC 20590 14. Sponsoring A g e n c y C o d e

NHTSA-- _15. S u p p l e m e n t a r y Notes Prepared in response to Section 9108 of U.S. Public Law 101-690.Based in part on research performed by CAE-Link Corporation under NHTSA ContractDTNH22-90-D-07010.

3 . R e c i p i e n t s Catalog NO .

5 . R e p o r t D o t e

May 10, 19916 . P e r f o r m i n g O rg a n i z a t i o n C o d e

NHTSA/NRD-538 . P e r f o r m i n g O rg a n i z a t i o n R e p o r t N O .

1 0 . Wo r k U n i t N o . (TRAIS)

11 . C o n t r a c t o r G r a n t N o .

13. Ty p e o f R e p o r t a n d P e r i o d C o v e r e d

1 6 . A b s t r a c t

This report reviews the problem of heavy vehicle speeding (in particular, speeding at greater than 65 mph)and speeding-related crash involvements. The report describes and assesses devices available to controltruck speed, and addresses the question of whether the use of speed control devices by heavy trucks shouldbe mandated. The report finds that, by all measures of crash involvement, speeding is not a significantfactor in the crash picture of single-unit trucks. Thus, most of the report addresses combination-unit trucks,which present a more complex picture.

Non-detectable radar studies show that highway speed limit compliance by combination-unit trucks is poor,but better than that of passenger vehicles. Most trucks that speed travel at just over the posted speed limit.Crash statistics indicate that speeding is generally less involved in combination-unit truck crashes than it isin passenger vehicle crashes. The report describes devices available to control truck speed, and ways thatthey are applied in commercial fleet settings. The report is supportive of fleet applications of speed-monitoring and speed-limiting devices, but concludes that there is not sufficient justification to considerrequiring all heavy trucks to be so equipped. Problem size statistics suggest that the number of targetcrashes is low, e.g., approximately 30 fatal crash involvements per year for combination-unit trucks. Thissmall crash problem size, together with uncertainties regarding the potential for crash reduction, suggestthat the benefits of mandatory speed limitation are questionable.

1 7 . K e y Wo r d s combination-unit trucks;speeding; high speed crashes;speed-limiting devices;road speed governors;speed-monitoring devices

1 8 . D i s t r i b u t i o n S t a t e m e n t

This document is available to the publicthrough the National Technical InformatioService, Springfield, VA 22161

I1 9 . S e c u r i t y Classif. (of t h i s r e p o r t ) 2 0 . S e c u r i t y Classif. ( o f t h i s p a g e ) 2 1 . N o . o f P a g e s 2 2 . P r i c e

61

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized


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COMMERCIAL MOTOR VEHICLE SPEED CONTROL DEVICES

TABLE OF CONTENTS

EXECUTIVE SUMMARY

1.0

1.1

1.2

1.3

1.4

1.5

1.6

2.0

2.1

2.2

2.3

2.4

INTRODUCTION

Problem Background

Overview of the Medium/Heavy Truck Crash Experience in the U.S.

Vehicle Speed and Crash Severity

Factors Influencing Truck Speeding

Programs to Improve Speed Enforcement

Overview of Report Organization

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TRUCK TRAVEL SPEED STATISTICS 2-l

Detectable vs. Nondetectable Radar: 1987 IIHS Study 2-l

Studies of Highway Travel Speeds Employing Nondetectable Measures 2-2

2.2.1 Pezoldt and Brackett (1989) 2-2

2.2.2 Mace and Herkard (1990) 2-4

2.2.3 Recent IIHS Studies 2-6

Motor Carrier Safety Survey 2-8

Summary and Conclusions 2-9

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Table of Contents

3.0

3.1

3.2 Fatal Accident Reporting System (FARS)Statistics 3-5

3.3 Problem Size Estimates: Speed-Monitoring and Speed-LimitingTarget Crash Involvements

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3.4 Summary of Available Crash Statistics

4.0

4.1

4.2

4.3

SPEED CONTROL MECHANISMS AND DEVICES

Study Methodology

Limitations of Speed Control Devices

Speed Monitoring Devices

STATISTICS ON HEAVY TRUCK SPEEDING-RELATED CRASHES

Selected State Statistics

3.1.1 States With 65 mph Maximum Speed Limits for Trucksand Passenger Vehicles (Florida and Georgia)

3.1.2 States With Differential Maximum Speed Limits forTrucks and Passenger Vehicles (Ohio and Virginia)

3.3.1 Problem Size Estimates: Speeding-Related Crashes

3.3.2 Problem Size Estimates: Speeding > 65 mph-Related Crashes


4.3.1 On-board Computers

4.3.2 Tachographs

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Table of Contents

4.4

4.5

4.64.7

5.0

5.1

5.2

5.3

5.4

5.5

5.6

5.7

6.0 CONCLUSIONS AND RECOMMENDATIONS 6-l

Engine Speed Governors

4.4.1 Mechanical Engine Speed Governors

4.4.2 Electronic Engine Speed Controls

Vehicle Road Speed-Limiting Devices

4.5.1 Vehicle-Controlled Devices (Road Speed Governors)

4.5.2 Driver-Controlled Devices (Cruise Controls)

Vendor StudiesSummary and Conclusions

FLEET APPLICATIONS

Study Method

Fleet Approaches to Speed Monitoring/Control

Driver Acceptance, and Device Tampering

Incentive Programs

Fleet Satisfaction

Fleet Studies

Conclusions Regarding Fleet Applications

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REFERENCES


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Heavy truck safety has improved dramatically over the past decade. The fatal crashinvolvement rate for medium/heavy trucks was 3.7 per 100 million vehicle miles of travel in

1988, an all-time low. Between 1977 and 1988, the fatal crash involvement rate forcombination-unit trucks decreased 40 percent, while the rate for passenger vehicles(cars/light trucks and vans) decreased only 25 percent. The efforts of motor carriers andtheir drivers, coupled with expanded state-Federal programs to license commercial driversand inspect vehicles at roadside, all seem to be having a positive effect.

Despite these encouraging findings and the efforts of most motor carriers and drivers tooperate responsibly, many motorists are uncomfortable sharing the highways with heavytrucks. These concerns are heightened when trucks speed, principally because of therelative size of trucks compared to passenger vehicles. Because of the size of trucks, truck crashes in general have a greater likelihood of causing a fatality than do passenger vehicle

crashes. As could be expected, the preponderance of these fatalities occur amongoccupants of the other, generally much smaller, involved vehicles, rather than among truck occupants.

In response to these concerns, it has been suggested that trucks should be required to beequipped with devices to control their maximum speed. This study examines the safetyissue of truck speeding and considers the merits of mandating the installation of speedcontrol devices on heavy trucks. Two principal forms of speed control are addressed: (1)speed-limiting devices (governors), which directly limit engine and/or road speed; and (2)speed-monitoring devices, which do not control vehicle speed directly, but rather provide acontinuous record of vehicle speed that may be used to determine if speeding has occurred.

In most states the speed limit for heavy trucks on rural Interstate highways is 65 mph.Heavy trucks, notably combination-unit trucks, which are the focus of most of the concern,accumulate much of their travel mileage on rural Interstate highways. Thus, if speed-limiting devices were required on heavy trucks, they would have to be designed to allow travelspeeds of at least 65 mph in order to permit trucks to travel at speeds up to the legal maximum.In this report, 70 mph is used as a hypothetical value at which speed-limiters might be set. Aspeed-limiter setting near 70 mph would permit trucks to travel at the speed limit on 65 mphroadways, with some added tolerance for additional power needed for hill-climbing or passing.Data are also provided relating to crashes occurring at speeds greater than 65 mph.

This report notes the fact that most heavy truck crashes do not occur on roadways where veryhigh travel speeds (e.g., greater than 70 mph) are prevalent. More than 90 percent of combination-unit truck crashes and 95 percent of single-unit truck crashes occur on roadwayswhere the speed limit is less than 65 mph, and where the incidence of truck speeding in excessof 70 mph or even 65 mph is low. Speed-limiting devices would have no effect on vehiclespeed or crash likelihood at travel speeds below their set point (e.g., 70 mph).


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Executive Summary

Moreover, speed-limiters would not control speeding on downgrades that are steep enough forthe vehicle to be in a free roll. In a free roll situation, vehicle speed is not determined byengine revolutions or gearing but rather by the force of gravity acting against the rolling

resistance of the vehicle. Because of the desire to maximize fuel economy, the rollingresistance of todays trucks is minimal, in particular when considered in relation to theirweights. Since high truck speeds on downgrades would not ordinarily be affected by speed-limiting devices, this report excludes on-grade crashes from the all target crash problem sizeassessments of crashes involving speeds greater than 65 mph.

The use of speed-monitoring devices--devices which provide a continuous record of vehiclespeed during a trip--may be applicable to a broader range of highway travel (i.e., 55 mph and65 mph highways), assuming that the individual monitoring the vehicle speed data knows theposted speed limit for the highway traveled. In consideration of this broader applicability of speed-monitoring devices, this report addresses truck speeding in general as well as speeding inexcess of the potential maximum speeds at which mandatory speed-limiting devices might be set(e.g., 70 mph).

For all vehicle types, driver compliance with posted highway speed limits is poor. However,when trucks do speed, it is typically at levels just over the speed limit. The extent of truck speeding in excess of 70 mph varies with the posted speed limit. On highways posted at 55mph, about 3 percent of trucks speed in excess of 70 mph. On roads posted at 65 mph, about14 percent of trucks exceed 70 mph. By comparison, about 10 percent of all passenger vehicles(cars and light trucks) exceed 70 mph on 55 mph highways, while about 23 percent exceed 70mph on roads posted at 65 mph.

Although commercial vehicle drivers are often under economic pressure to move goods quicklyand thus possibly to speed, there are also significant economic incentives not to speed. Fuelusage and engine maintenance requirements are considerably less when speeds of less than 65mph are maintained. Multiple speeding citations for offenders can lead to commercial driverslicense suspension--an economic catastrophe for most drivers. Moreover, a cooperativeFederal-state program, the Commercial Drivers License (CDL) Program, now exists to preventdrivers from obtaining multiple licenses and/or accumulating multiple speeding convictions indifferent states with impunity.

Police accident report data suggest that comparatively few heavy truck crashes involve truck travel speeds in excess of 70 mph. Only about 0.2 percent of all combination-unit truck crashinvolvements, and 0.7 percent of fatal crash involvements, occur at police-reported estimatedtravel speeds in excess of 70 mph. By comparison, about 0.5 percent of all passenger vehiclecrash involvements, and about 6 percent of fatal crash involvements, occur at estimated speedsin excess of 70 mph. In 1988-89, there was an average of approximately 30 combination-unittruck fatal crash involvements where a vehicle travel speed in excess of 70 mph was noted bythe investigating police officer. In comparison, there were an average total of 4,063combination-unit truck fatal crash involvements at all travel speeds. There were 3,614

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Executive Summary

involvements of all vehicle types (mostly passenger vehicles, but including trucks) in fatalcrashes where the vehicle was traveling at speeds greater than 70 mph. Thus, high-speed truck

crashes represent a small proportion of both the overall truck crash picture (0.7 percent) and theoverall high-speed crash problem (0.8 percent).

Involvement rates in speeding-related crashes are also relatively low for combination-unittrucks. For example, the combination-unit truck involvement rate for all crashes with police-reported speeds of greater than 70 mph was on the order of 0.3 per 100 million vehicle milestraveled (VMT) in 1988-89. The comparable statistic for passenger vehicles was approximately2.4 per 100 million VMT. For fatal crash involvements, the estimated rates were 0.03 per 100million VMT for combination-unit trucks and 0.19 for passenger vehicles.

Another statistical approach to assessing the role of speeding and speeding in excess of 65 mph

in heavy truck crashes is to derive the average number of relevant crash involvements per 1,000vehicles. This is, in essence, a measure of the annual l ikelihood that a vehicle will be involvedin a relevant crash. Annually, approximately 0.18 combination unit trucks per 1,000 registeredare involved in a crash at a police-reported travel speed of greater than 70 mph, whereas thecomparable figure for passenger vehicles is 0.25. The likelihood statistics are more similarfor trucks and passenger vehicles than are the "rate"statistics. This is due to the greaterexposure of combination-unit trucks to crash risk; on average, these vehicles travel six times asmany miles per year per vehicle than do passenger vehicles, and 10-15 times more miles on 65mph highways.

The speeding-related crash picture for single-unit trucks is very different from that of eithercombination-unit trucks or passenger vehicles. By all statistical measures, the numbers of crashes involving single-unit trucks exceeding the posted limit, speeding in excess of 65 mph, orspeeding at higher speeds are low. For example, the annual probability that a single-unit truck will be involved in a crash involving a police-reported speed in excess of 70 mph is on theorder of 1 in 33,000 (i.e., 0.03 involvements per 1,000 vehicles).

An important caveat relating to all speeding-related crash statistics cited in this report is that thecategorization speeding-related or high-speed related does not necessarily assure thatspeeding was the primary cause of the crash or any resulting fatalities. Virtually all crashesinvolve multiple contributing factors. The elimination of any one factor--e.g., high speed--mayor may not prevent the crash. Thus, the speeding-related and high-speed-related crashesidentified in this report should actually be viewed as potential target crashes for speed controldevices. Although speed control devices (if not tampered with) are likely to reduce the highwayspeeds of those trucks that do speed, their effectiveness in preventing and/or reducing theseverity of these potential target crashes is unknown.

Speed-limiting devices include mechanical engine speed governors, cruise controls, road speedgovernors, and electronically-controlled engines with transmission/rear axle/tire ratios designedto physically limit vehicle speed. All these approaches have limitations. First, as noted, none

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Executive Summary

of these devices can effectively control downhill vehicle speeds. Truck speeding-related crashesinvolving downgrades, where the vehicle was in a free-roll, would be unaffected by speed-

limiting devices. Mechanical engine speed governors limit the engines maximum speed, but donot limit the vehicles top speed unless the engine is matched with a transmission and rear axlegeared to also limit top speed. Even then, conventional engine speed governors allow theengine to overshoot and thus attain higher than rated vehicle speeds. Cruise controls must be .activated by drivers and, therefore, can be set at speeds higher than 65 mph or simply not beactivated. Road speed governors, devices that monitor and control actual vehicle speed, caneffectively limit truck speed. However, most designs are only tamper-resistant; none aretamper-proof. A determined truck driver or truck owner can defeat these devices.

The Environmental Protection Agencys heavy duty engine emission control regulations requiremore stringent emissions standards in the 1991 model year, with further emissions reductions

required beginning with the 1994 model year. New truck diesel engines developed to meet the1991 standards, and under development to meet the 1994 standards, include electronic controlson engine speed. These electronic controls are intended primarily to ensure that emissionsstandards are met, but they have the ancillary benefits of improving fuel economy and providinga means of limiting maximum vehicle speed. Thus, a speed-limiting capability is already beingbuilt into new heavy duty vehicle engines. This road speed limitation is accomplished byreducing engine RPMs as road speeds approach the governed limit. In order to maximize fueleconomy and meet EPAs emissions standards, most buyers specify engine/drivetrain gearingcombinations with optimal cruising speed ranges of 55-65 mph. Optimal specifications for agiven buyer are dependent on such factors as type and size of loads carried, predominantroadway types traveled, and desired fuel economy. Market penetration of the new engines will

increase by approximately 7-10 percent annually until fleet turnover is virtually complete in theearly 2000s.

Speed monitoring/recording can be accomplished with a variety of electronic and mechanicaldevices and can be an effective tool for fleet managers in their efforts to responsibly control theoperation of their vehicles. Equipping a truck with a speed recorder does not guarantee,however, that it will be operated within speed limits. Active management involvement inmonitoring and following up on data provided by speed recorders is critical to theireffectiveness. Moreover, the incremental benefits of installing speed-monitoring equipment maybe questionable for those fleets where management practices are already in place to minimizespeeding. In spite of these limitations, many fleets currently use speed monitors and are

generally satisfied that they are worthwhile. However, no systematic fleet test data wereidentified to document the actual effectiveness of such devices in reducing crash involvement.

A speed-monitoring system that includes external electronic ports whereby enforcement officialscould obtain direct roadside access to truck trip speed data is technically feasible. However,such a system would require elaborate system specifications, industry-wide standardization, andsubstantial equipment investments by both motor carriers and enforcement officials. Moreover,this enforcement concept raises significant constitutional, legal, and operational issues.

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Executive Summary

Resolution of these concerns would necessarily have to precede any policy decision requiringthe installation of speed-monitoring devices.

Based on the findings of this study, the agency concludes that the Federal mandating of speedcontrol devices on combination-unit trucks does not appear to be justified at this time. Problemsize statistics suggest that the number of target crashes is low, especially when viewed againstthe overall truck crash picture or against the overall problem of highway speeding. Speed-limiting devices would not dramatically change the distribution of truck speeds on the highways,since most trucks now travel at speeds below levels likely to be set by the devices, and thosethat are currently traveling at higher speeds are typically traveling at speeds just a few miles perhour higher. It is not certain whether the marginal reduction of speed for these vehicles wouldactually reduce their crash risk (or resulting fatality risk) significantly, since other, nonspeed-related driver errors may still occur and cause similar crashes and injuries. For all of thesereasons, the potential effectiveness of mandatory speed limitation in terms of either crashreduction or lives saved is questionable.

Numerous, complementary approaches to truck speed control are already operative at the levelsof vehicle design, fleet management practice, and driver licensing. Two current trends inparticular--the development and market penetration of electronic engine controls and theestablishment of the Commercial Drivers License Program--are expected to further mitigateagainst truck speeding. The CDL Program targets flagrant and/or repeat speeding offenders,the same operators who would be most likely to defeat or circumvent mandatory speed-limitingdevices.

All motorists--commercial and private vehicle operators alike--need to do a better job of voluntarily complying with posted speed limits on highways. Highway speeding appears to be awidespread highway safety concern that is not limited to commercial motor vehicles. Publicinformation and education programs, coupled with increased speed enforcement (for all vehicletypes) may be the best method of achieving improved highway speed limit compliance.

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1.0 INTRODUCTION

The National Highway Traffic Safety Administration (NHTSA) has prepared this report onheavy truck speed control devices in response to Section 9108 of the Truck and BusRegulatory Reform Act of 1988, Public Law 101-690, dated November 18, 1988, whichreads as follows:

The Secretary shall conduct a study on whether or not devices which control thespeed of commercial motor vehicles enhance safe operation of such vehicles . . . (and). . .not later than thirty months after the date of enactment of this Act, ... shall submitto Congress a report on the results of the study . . . together with recommendations . . .on whether or not to make the use of speed control devices mandatory forcommercial motor vehicles.

The commercial vehicles addressed in this report are medium and heavy trucks (GrossVehicle Weight Rating > 10,000 lb.), with emphasis on combination-unit trucks (tractortrailers).

1.1 Problem Background

The Surface Transportation and Uniform Relocation Assistance Act of April 1987 allowedstates to increase the speed limits on rural Interstates from 55 miles per hour (mph) to 65mph. In 1987-88, 40 states instituted 65 mph limits for rural Interstates, some withrestrictions on medium/heavy trucks (e.g., a lower speed limit such as 55 mph for trucks).The majority of the Interstate highway system in rural areas is now posted at 65 mph fortrucks and other vehicles.

Many vehicles of all types regularly travel at highway speeds greater than the posted speedlimit. This poor speed limit compliance, coupled with the size differential between largetrucks and passenger vehicles, has raised the question of whether there would be significantsafety gains from the limitation of truck highway speeds. Devices that prevent or minimizetruck speeding include those that limit maximum vehicle speed (governors) and those thatmonitor and record vehicle speed. Speed governors would, in most cases, need to be set at65 mph or greater (a hypothetical value of 70 mph is used here), since any governor set

below 65 mph would prevent the vehicle from traveling at the legal speed limit on 65 mphroadways.

Speed recording devices, though not a direct speed control, are also available to help fleetmanagers monitor the speed limit compliance of their drivers. Monitors are potentiallyapplicable to achieving speed compliance on 55 mph roadways (or even lower-speedroadways) as well as 65 mph roadways when managers know the speed limits on theroadways traveled by their fleet vehicles.


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1. Introduction

To assess the safety importance of truck speeding and potential benefits of speed controldevices, this report first assesses the incidence of truck speeding and its relation to truck

crashes. The report focuses on the prevalence of truck speeding and crashes at speedsgreater than 65 mph, since they would be the prime targets of speed control devices. Dataare also presented relating to speeding at speeds below 65 mph, since speed monitors couldbe applied to that problem. Following the presentation of statistics on speed complianceand speeding-related crashes, the characteristics and current and potential applications of truck speed-limiting and monitoring devices are addressed. From this, recommendationsare offered on ways to improve fleet speed limit compliance and regarding the question of whether the use of truck speed-limiting devices should be made mandatory in the UnitedStates.

1.2 Overview of the Medium/Meaw Truck Crash Experience in the U.S.Before addressing safety considerations relevant to truck speeding, it is worthwhile toreview the overall truck accident picture . Table P-l presents an overview of themedium/heavy truck police-reported crash experience in the United States based on datafrom the NHTSA General Estimates System (GES), Fatal Accident Reporting System(FARS), and Federal Highway Administration (FHWA) statistics on annual vehicle milestraveled (VMT) and vehicle registrations. Comparative statistics are provided forcombination-unit trucks, single-unit trucks, and passenger vehicles, which, for the purposesof this report, are defined as all vehicles other than medium/heavy trucks. Approximately97 percent of the passenger vehicle category consists of automobiles and light trucks/vans.Motorcycles, buses, and other miscellaneous vehicles are included in the passenger vehiclecategory. Throughout this report, crash statistics are, when possible, presented separatelyfor combination-unit trucks and single-unit trucks, since the crash experiences of thesevehicle types are very different from each other.

The data indicate that single-unit trucks are significantly under-involved in crashes relative toother vehicle types. This is true for all measures of crash involvement shown, with the oneexception of overall crash involvement rate, which is similar for single-unit and combination-unit trucks.

The crash involvement picture for combination-unit trucks is considerably more complex.Combination-unit trucks constitute 0.8 percent of registered vehicles, but represent 1.9 percentof motor vehicle involvements in police-reported crashes. Furthermore, they constitute 6.6percent of motor vehicle involvements in fatal crashes. Combination trucks travel on averagemore than 60,000 miles per year, compared to about 10,000 miles for the average passengervehicle. They have a far greater exposure than other vehicle types to the possibility of involvement in a crash, and this increased exposure contributes to their overrepresentation infatal crashes.

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1. Introduction

Combination-unit trucks have a police-reported crash involvement rate of 244.0 per 100 millionvehicle miles traveled (VMT),which is less than half the rate for passenger vehicles. However,

the fatal crash involvement rate of combination-unit trucks (4.5 per 100 million VMT) is greaterthan that of passenger vehicles (3.0 per million VMT).

The number of combination-unit truck crash involvements per 1,000 vehicles per year is morethan twice that of passenger vehicles, and nearly five times that of single-unit trucks. Thenumber of combination-unit truck involvements in fatalcrashes per 1,000 vehicles isapproximately nine times higher than that of passenger vehicles or single-unit trucks.

Table l-l: Summary of the U.S. Medium/Heavy Truck Crash Experience in Relation to Other Vehicles

Statistic Vehicle Type: Comb-Unit Trks Sngl-Unit Trks Pass. Vehs.

Annual Vehicle Involvements in Fatal Crashes

Annual Fatal Crash InvolvementsPer 1,000 Vehicles

2.8 0.3 0.3

Notes: 1) Passenger Vehicles are here defined as all vehicles other than combination-unit or single-unitmedium/heavy trucks. The passenger vehicle category includes approximately 97 percent automobiles and lighttruck/vans, and approximately 3 percent miscellaneous vehicles such as buses and motorcycles. 2) Thedistinction between vehicle involvements in crashes and crashes is noteworthy. A particular crash may involvea single vehicle or multiple vehicles. For example, in 1988-89 there was an annual average of 41,418 fatalcrashes involving 61,726 vehicles. The average number of persons killed was 46,324.

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1. Introduction

Not shown in Table 1-1 is the distribution of fatalities resulting from combination-unit truck crashes (statistics not shown in Table 1-1). In 1988-89, there were an average of 4,063

combination-unit truck fatal crash involvements, resulting in 4,494 fatalities. Of these, 3,742(84.4 percent) were either non-occupants (e.g., pedestrians) or occupants of other involved -vehicles; 702 (15.6 percent) were truck occupants (drivers or passengers).

Combination-unit trucks accumulate about 49 percent of their mileage on the Interstatehighway system, versus 22 percent for single-unit trucks and 20 percent for passengervehicles. The Interstate highway system has the lowest fatal crash rate of all major roadtypes (1988 FARS Annual Report). For example, only about 26 percent of combination-unit truck involvements in fatal crashes occur on Interstate highways (FARS, 1988) apercentage considerably lower than the exposure percentage (49 percent) cited above. Forboth single-unit trucks and passenger vehicles, the percentage of involvements occurring on

Interstate highways is about 10 percent (FARS, 1988).On rural Interstate highways, which now are generally 65 mph highways (and representvirtually the only 65 mph highways in the United States), the exposure differences betweencombination-unit trucks and other vehicle types are even more striking. Combination-unittrucks accumulate 31 percent of their mileage on rural Interstate highways, an average of about 19,000 rural Interstate miles per vehicle. Single-unit trucks are driven 11 percent of their mileage on rural Interstates (about 1,400 miles per vehicle), and passenger vehiclesare driven only 8 percent of their miles on rural Interstates (about 800 miles per vehicle).

The above differences in exposure to 65 mph roadways are reflected in vehicle typedifferences in their proportions of crash involvements occurring on roadways with differentspeed limits. Table 1-2 shows the distribution of crash involvements and fatal crashinvolvements by roadway posted speed limit for the three vehicle type categories.

Not all rural Interstate highways have 65 mph speed limits, particularly for trucks. At thiswriting, approximately 90 percent of rural Interstate miles are posted at 65 mph for cars,and approximately 56 percent are posted at 65 mph for trucks. Combination-unit trucksaccumulate a large percentage of their mileage on these roadways, which have the lowestoverall crash rates of any major roadway class (Shelton, 1990). These low crash rates arereflected in the relatively low percentage of combination-unit truck crashes that occur on 65mph highways (6.4 percent) relative to combination-unit truck exposure on these highways(approximately 56 percent of 31.2 percent, or 17 percent). Ironically, however, public safetyconcerns regarding vehicle speeding are perhaps greatest in relation to the Interstatehighway system (e.g., NHTSA, 1989; McKnight Klein, and Tippetts, 1989).

A final notable trend regarding heavy truck safety is the dramatic decreases in crash ratesover the past decade. The fatal crash involvement rate for all medium/heavy truckscombined was 3.7 per 100 million vehicle miles of travel in 1988, an all-time low. Between1977 and 1988, the fatal crash involvement rate for combination-unit trucks decreased 40

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1. Introduction

percent and the rate for single-unit trucks decreased by close to one-third, whereas the ratefor passenger vehicles (cars/light trucks and vans) decreased only 25 percent. The effortsof motor carriers and their drivers, coupled with expanded state-Federal programs tolicense commercial drivers, and inspect vehicles at roadside, all seem to be having apositive effect on truck crash involvements.

Table 1-2: Crash Involvements and Fatal Crash Involvements by Posted Speed Limit

Annual Crash Involvements

Annual Fatal Crash Involvements(FARS, 88-89 Avg)

4,063 1,051 56,612

Fatal Crash Involvements,PSL = 65 mph Column %

568 33(14.0%) (3.1%)

2,415(4.3 %)

Fatal Crash Involvements, 2,400 516 26,06555< =PSL< =64 mph Column % (59.1%) (49.1 %) (46.0%)

Fatal Crash Involvements, 1,095 502 28,191PSL < =54 mph Column % (27.0 %) (47.8%) (49.7 %)

Note: Data represent all GES and FARS crash involvements. Cases with unknown posted speed limits (34.2percent of GES cases, 2.4 percent of FARs cases) have been proportionately allocated among the three PSLcategories.

1.3 Vehicle Sseed and Crash Severity

Truck speeding--indeed, speeding by any vehicle--is a concern because of the strong relationshipbetween vehicle speed and occupant injury severity. Studies of occupant injuries (e.g.,Malliaris, Hitchcock, and Hedlund, 1982) have shown that the principal determinant of occupanttrauma level resulting from a collision is the change of vehicle speed upon impact, or Delta V.This relationship is shown in Figure P-l.

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I. Introduction

50

45

40

35

30

25

20

15

10

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020 30

CRASH SEVERITY (MPH)

Figure 1-1: Relationship between passenger vehicle crash severity (Delta V)and vehicleoccupant injury/fatality probability (Malliaris, 1982, based on data from the NationalCrash Severity Study; AIS 3 + injuries are those that are serious or of greater severity on the 6-point Abbreviated Injury Scale)

Delta V is not the same as precrashvehicle travel speed. Some braking may occur beforeimpact, and often much deceleration occurs after impact as vehicles roll or slide to a stop.Many crashes occurring on high-speed roadways involve relatively low Delta Vs (e.g.,

sideswipes). Nevertheless, high vehicle travel speeds create the potential for high Delta Vs in acollision. And, the relationship shown in Figure 1-1 (for a sample of passenger vehiclesinvolved in crashes) demonstrates that higher Delta Vs are associated with greatly increasedinjury potential.

l

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1. Introduction

1.4 Factors Influencing Truck heeding

.

Commercial vehicle drivers are often under pressure to move goods as rapidly as possible. Formany operators, the adage time is money holds much truth. Long-haul trucks operate in ahighly competitive environment where shippers may demand very tight delivery schedules. Thecurrent trend toward just-in-time delivery is economically attractive to manufacturers anddistributors, but can result in added schedule pressure on truckers.

Long-haul trucks compile the vast majority of their miles on highways, principally Interstates.Speed limit compliance on these roadways is poor for all vehicle types. On most highways, themajority of vehicles exceed the posted speed limit (Pezoldt and Brackett, 1989; see Chapter2). Thus, if compliance with highway speed limits were equivalent for trucks and cars (i.e.,if trucks were just keeping up with traffic), trucks would still have a much greaterexposure to high speed driving situations. Chapter 2 of this report provides data whichshow that trucks are generally more compliant with highway speed limits than are cars, anddata presented in Chapter 3 indicate that a smaller percentage of their involvements incrashes are speed-related. But trucks have a far greater exposure than other vehicles tohigh speed highway situations. This increases their l ikelihood of involvement in a speed-related crash during any given time period.

A factor contributing to truck speeding is detection by truck drivers of enforcement efforts.The resourceful tactics used by some long-haul truck drivers to avoid speed limitenforcement by police are well known. Virtually all long-haul trucks are equipped with CBradios, which can be used to evade police speed limit enforcement efforts. In addition,

studies indicate that roughly one fourth of combination-unit truck tractors are equippedwith radar detectors (see Section 2.1).

Opposed to the above factors are a number of other factors acting to prevent long-haultrucks from speeding. The time is money factor is counterbalanced to some extent byeconomic incentives for speed compliance relating to fuel economy, vehicle maintenanceeconomy, and insurance/crash costs. For example, fuel economy improves by roughly 1percent for each 1 mph reduction in speed in the 55-70 mph range for conventional dieseltrucks (estimated from Weiss et al, 1982).

Professional truck drivers also have a strong economic incentive to avoid speeding citations.

Multiple speeding citations can lead to commercial drivers license suspension -- aneconomic catastrophe for most drivers. Moreover, a cooperative Federal-state programnow exists to ensure that only one commercial drivers license is issued to any individual,and that convictions for certain traffic violations committed in a commercial motor vehicleoccurring anywhere in the United States are reported to the licensing state and made a partof the drivers record. This system, termed the Commercial Drivers License InformationSystem (CDLIS), is a critical component of the entire Commercial Drivers License (CDL)program. This program provides a mechanism for the exchange of information among

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1. Introduction

states in order to prevent drivers from obtaining multiple licenses and/or accumulatingmultiple speeding convictions in different states with impunity. Section 1.5 belowspecifically addresses this program and describes its potential effects on drivers with seriousspeeding violations.

There are also public relations incentives relating to speed compliance and safe driving ingeneral. A majority of combination-unit trucks have their company names prominentlydisplayed on the trailer and/or the tractor cab, and many vehicles display an explicit signwith a statement such as, If you see this vehicle operated unsafely, please call xxx-xxx-xxxx.In these respects, many commercial vehicle drivers, unlike private vehicle drivers, areconstantly under public surveillance, with a resultant possibility of sanctions for unsafedriving acts.

Many trucking fleets are organized to permit some degree of management control overvehicle highway speeds, independent of any mechanical or legal speed-limiting factors.Records are maintained of vehicle travel times between terminals, fuel economy,maintenance record, complaints of the public or other drivers, and other data that may berelevant to speeding by drivers. Some fleets even employ their own road patrols to identifyunsafe drivers. At a management level, there are strong economic incentives forminimizing accident rates, in particular those involving unsafe driving acts by drivers.

Finally, a major topic addressed in this report is the use of electronic and mechanicaldevices to limit truck speed. This includes speed-limiting devices such as engine speedgovernors--mechanisms built into the engine that limit engine revolutions per minute (rpm).The new generation of electronically-controlled engines have speed-limiting capabilities thatgreatly enhance the ability of fleet managers to prespecify the maximum cruising speeds of their vehicles. In addition to engine speed governors, there are supplemental devices suchas cruise control that limit truck speed.

Also addressed are monitoring devices such as on-board computers which provide acontinuous record of vehicle speed. Monitoring devices do not directly limit vehicle speedbut may be used to indirectly control speeds by providing fleet management with acontinuous record of vehicle speed. Moreover, monitoring may be applied to controllingspeeds on both 65 mph and 55 mph roadways, if the roadway speed limits are known bymanagement. The speed-reduction effectiveness of speed monitoring is predicated,however, on a review of the continuous speed record by management or some other

authority.

In summary, while there are economic and other disincentives for speed compliance bytruck drivers, there are also very strong incentives for speed compliance. At the fleetmanagement level, there are a number of means available to monitor and control fleethighway speeds. A pervasive theme of this report is that much responsibility falls on fleet

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1. Introduction

management for initiating and sustaining efforts, be they device-related or purelymanagerial, to maximize speed limit compliance by their drivers.

1.5 Programs to Improve Speed Enforcement: Commercial Drivers License Programand Commercial Vehicle Enforcement Pilot Project

The principal goal of the Commercial Motor Vehicle Safety Act of 1986 was to improvehighway safety by ensuring that drivers of large trucks and buses are qualified to operatethose vehicle on the highway. The Act retained each states right to issue a commercialdrivers license (CDL) but established minimum Federal standards which states must meetwhen licensing commercial motor vehicle drivers.

The Federal Highway Administration (FHWA) is currently working with the states and theDistrict of Columbia to implement the CDL program. As of March 1, 1991, 34 licensing

jurisdictions are issuing CDLs. The Act requires that all commercial motor vehicleoperators have a CDL by April 1, 1992.

A critical component of the CDL program is the disqualification of commercial drivers forconviction of certain offenses committed while driving a commercial motor vehicle. Thesedisqualifications (loss of driving privileges) may range in length from 60 days to life,depending on the nature and number of recurrences of the offense. For example, a drivercan be disqualified for 60 to 120 days for conviction of two or more serious trafficviolations within a three-year period. Serious traffic violations include improper orerratic lane changes; reckless driving; following too closely; and, most relevant to thisreport, excessive speeding (defined as 15 mph or more in excess of the posted speed limit).

For driver disqualification purposes, convictions for out-of-state violations are treated thesame as convictions for violations committed in the home state. State participation in theCDL program and its licensing/violations database, the Commercial Driver LicenseInformation System (CDLIS), ensures that any conviction a driver receives outside his orher home state will be transmitted to the home state so that disqualifications are enforced.Convictions for traffic violations committed in a commercial motor vehicle become part of the drivers permanent driving record.

This cooperative Federal-state program now functions as an enforcement backstop to theother speed control approaches--e.g., speed control devices and fleet managementapproaches--addressed in this report. In the context of truck speeding, the most importantcontribution of the CDL program is the disqualification of chronic and/or flagrant speedingoffenders from commercial motor vehicle operation.

Complementing the CDL program are initiatives intended to enhance speed limitcompliance enforcement on the highways. For example, the Commercial Vehicle

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1. Introduction

Enforcement Pilot Project (CVEPP) is a joint effort involving NHTSA, FHWA, theCalifornia Highway Patrol (CHP), and other state and local government jurisdictions.

CVEPP is intended to reduce truck crashes through heightened public and industryawareness of local truck safety problems and identification and promulgation of successfulstrategies to enhance ongoing commercial vehicle enforcement efforts. CVEPP is orientedtoward the mitigation of primary collision-causing commercial motor vehicle violations onhighways (e.g., Interstates); speeding is one of the principal moving violations resulting inenforcement stops and safety inspection. Currently, there are CVEPP sites in six states.Enforcement methods tested and refined during the pilot program are expected to beimplemented on a national scale in cooperation with participating local and state

jurisdictions in the coming decade.

1.6 Overview of Report Organization

The remainder of this report is organized to address the following major issues andquestions regarding commercial vehicle speed control:

How good is the highway speed limit compliance of heavy commercial vehicles?How does it compare to other vehicles?

To what extent are speeding and, specifically, speeding at greater than 65 mphand 70 mph, involved as causal or contributing factors in traffic crashes? Howdoes the level of speeding involvement for trucks compare to that of passenger

vehicles?

What electromechanical devices are available to control truck speed? How cantrucks be designed to provide built-in limitations to maximum vehicle speed?

How do fleet managers use speed control devices? What managementapproaches are most effective in ensuring speed compliance by drivers?

Should the use of speed control devices--speed-limiting and/or speedmonitoring--be mandated on medium/heavy trucks?

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2.0 TRUCK TRAVEL SPEED STATISTICS

This chapter presents statistics on the prevailing highway travel speeds of heavy trucks andother vehicles. It addresses the incidence of truck speeding and speeding over 65 mph and 70mph, and compares statistics on the highway travel speeds of trucks to those of other vehicles.Virtually all of the highway observations reported were taken at level sites; thus, the data citeddo not reflect downhill truck speeds, which may be significantly greater than speeds on levelterrain or on upgrades. However, downhill speeds are not of particular interest here sincespeed-limiting devices would not affect truck free-roll downhill speeds.

2.1 Detectable vs. Nondetectable Radar: 1987 IIHS Study

Studies of vehicle travel speeds employing conventional radar systems are likely to yieldestimates of highway travel speeds that are spuriously low. This is because a significantnumber of vehicles, especially heavy trucks, are equipped with radar detectors. Vehicles soequipped will typically slow down when they encounter an active radar system, thus invalidatingconventional radar measurements.

The Insurance Institute for Highway Safety (1987) reported research performed in Virginia andMaryland showing that 11 percent of speeding vehicles (i.e., vehicles traveling at greater thanor equal to 62 mph in a 55 mph zone) slowed by at least 5 mph when a police radar wasactivated. Twenty-five percent of the combination trucks slowed down, indicating that a much

larger percentage of combination trucks were equipped with radar detectors. From thesestatistics and other reports of frequent radar detector use in combination trucks, one mayconclude that conventional radar studies of travel speeds underestimate both the absolute numberof heavy trucks that speed, and their relative likelihood of speeding compared to other vehicles.

Although a larger percentage of heavy trucks are equipped with radar detectors, studiesemploying nondetectable radar provide no indication that heavy trucks actually travel at higherhighway speeds than do passenger vehicles. For example, Table 2-1, based on the same seriesof tests, compares the travel speeds of different vehicle types as measured by nondetectableradar versus conventional detectable police radar. The difference between the detectable andnondetectable conditions was greatest for combination-unit trucks, suggesting that a largerpercentage are equipped with radar detectors. Nevertheless, a comparison of vehicle types inthe nondetectable radar condition does not indicate that tractor-trailer travel speeds are higherthan those of other vehicle types. The percentage of combination-unit trucks traveling at> 65 mph was slightly higher than that of passenger cars, however.


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2. Travel Speed Statistics

2.2 Studies of Highway Travel Speeds Employing Nondetectable Measures

2.2.1 Pezoldt and Brackett (1989)

Pezoldt and Brackett (1989) reported more extensive data comparing the highway speeds of trucks and other vehicles as measured by detectable versus nondetectable radar at 14 locations infour states. The vast majority of the trucks in the Pezoldt and Brackett study werecombination-unit trucks. All data were collected during daylight hours. Corroborating the IIHSstudy cited above, their data suggest that many more heavy trucks than other vehicles areequipped with radar detectors.

TABLE 2-l: AVERAGE TRAVEL SPEEDS AND PERCENTAGE OF VEHICLES TRAVELING AT ASPEED OF > 65 MPH FOR VARIOUS VEHICLE TYPES A MEASURED BYNONDETECTABLE AND DETECTABLE POLICE RADAR. (Data collected in late 1986 on14 55 mph highways in Maryland and Virginia; Insurance Institute for Highway Safety, 1987)

AVE RAG E SP EED PERCENT > 65 MPH

Passenger Cars

Sport/Spec Cars

Light Trucks

Heavy Single-UnitTrucks

Combination-UnitTrucks

Nondetectable Detectable Difference Nondetectable DetectableRadar Radar Radar Radar

60.2 59.9 - 0.3 16.1% 15.8%

61.4 59.7 - 1.7 23.7% 17.9%

59.8 59.0 - 0.8 15.2% 13.3 %

% Change

- 24%

- 16%

Nondetectable radar measurements showed that both trucks and passenger vehicles frequentlytraveled at speeds exceeding posted limits and 65 mph. However, the majority of the datasuggested that trucks travel at a high speed less frequently than do passenger vehicles. Table2-2 was compiled from Pezoldts and Bracketts nondetectable radar observations to show thepercentage of trucks and passenger vehicles traveling at speeds greater than the posted speedlimit (generally 55 mph) and the percentage traveling at greater than 65 mph. For both vehicletypes, the percentages varied greatly, reflecting local roadway, traffic, and enforcementconditions. At most locations, a greater percentage of passenger vehicles than trucks traveled atspeeds above the posted speed limit. Overall, under 11 conditions where the posted speed limitwas the same for trucks and passenger vehicles, the weighted mean percentages for trucks(N = 2,493) were 64.6 percent exceeding the posted speed limit and 15.6 percent exceeding

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65 mph. For passenger vehicles (N = 5,294), the corresponding percentages were 75.7percent and 29.2 percent. The data shown in Table 2-2 indicate poor compliance with

posted speed limits for both trucks and passenger vehicles; however, compliance is betteramong trucks than among passenger vehicles.

2.2.2 Mace and Heckard (1990)

Mace and Heckard (1990) reported on truck and passenger vehicle speed characteristicsafter the 65 mph speed limit was implemented on rural Interstates. Data were collected infour states which had raised the nontruck rural Interstate speed limit from 55 mph to 65mph. Data from two states (Illinois and California) which maintained the 55 mph speedlimit for trucks were compared to data from two states (Alabama and Arizona) whichincreased the truck speed limit to 65 mph. Speed measurements were taken in 1989 at 24rural Interstate sites. Summary statistics of the results are shown in Table 2-3.

TABLE 2-3: TRUCK AND PASSENGER VEHICLE MEAN TRAVEL SPEEDS AND PERCENT OFVEHICLES EXCEEDING 55 MPH AND 65 MPH AT 24 SITES IN 4 STATES. (All four stateshave 65 mph speed limits for passenger vehicles. Illinois and California have 55 mph speed limitsfor trucks; Alabama and Arizona have 65 mph speed limits for trucks; Mace and Heckard, 1990)

CA 4

SL Avg TS % > 55

Trk: 55 Trk: 58.32 Trk: 74.6%

PV: 65 PV: 63.43 PV: 88.3%Trk:PV:

55 Trk :65 PV:

57.18 Trk:65.25 PV:

Trk:PV:

65 Trk:65 PV:

64.68 Trk:68 .55 PV:

95.8%98.1%

Trk:PV:

65 Trk:65 PV:

64.90 Trk:68 .43 PV:

% > 65

Trk:

PV:

12.3%

36.1%Trk:PV:

12.6%49.1%

Trk:PV:

38.4%69.6%

Trk: 46.8%PV: 71.7%

Major findings apparent in Table 2-3 include the following:

l Speed limit compliance was poor (generally less than 50 percent) for bothvehicle types.

l Trucks exhibited lower average travel speeds, a lower percentage of vehiclesexceeding 55 mph, and a lower percentage of vehicles exceeding 65 mph thandid passenger vehicles. This was true in all four states.

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2. Travel Speed Statistic

l Average truck highway speeds were lower in the two states (Illinois andCalifornia) with 55 mph speed limits for trucks than they were in the two states(Alabama and Arizona) with 65 mph speed limits for trucks.

. In states with uniform speed limits (i.e., 65 mph for both trucks and passengervehicles), average truck travel speeds were 3-4 mph lower than passengervehicle travel speeds. The percentages of trucks exceeding the speed limit weresmaller than those for passenger vehicles.

l In the two states with differential speed limits for trucks and passenger vehicles(Illinois and California), truck compliance with the 55 mph speed limit waspoor. About 75 percent of trucks exceeded the 55 mph speed limit.

l In the two states with uniform speed limits (i.e., 65 mph for both trucks andpassenger vehicles), the percentages of trucks exceeding the speed limit werelower than those for states with differential speed limits. The percentages were38.4 percent in Alabama and 46.8 percent in Arizona.

Mace and Heckard (1990) also measured truck and passenger vehicle speeds at 18 localspillover sites in four states: Alabama, Arizona, California, and Tennessee. The spilloversites were on rural arterials posted at 55 mph and located near rural Interstates where thespeed limit for passenger vehicles was 65 mph and for trucks was either 55 mph(California) or 65 mph (Alabama, Arizona, Tennessee). Toward sites were those wheretraffic was on the arterial traveling toward the Interstate; away sites were those where

traffic was traveling away from the Interstate. Table 2-4 shows the results.

TABLE 2-4: AVERAGE TRUCK AND PASSENGER VEHICLE TRAVEL SPEEDS AT LOCAL SPILLOVERSITES (Mace and Heckard, 1990)

Avg PV TSAway

57.6

59.6

59.1

56.2

57.3

58.1

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Key results of the spillover site study (see Table 2-4) were as follows:

l In all four states and at both toward and away sites, average truck speedswere lower than average passenger vehicle speeds. .

. With one exception (trucks at the California site), average away travel speedswere slightly higher than toward travel speeds.

l The California site exhibited the lowest average truck speeds in both thetoward and away conditions. California was the only state of the four wherethe truck speed limit on the nearby Interstate was 55 mph instead of 65 mph.

2.2.3 Recent IIHS StudiesThe Insurance Institute for Highway Safety (IIHS) has conducted time series studies of highway travel speeds in a number of states to determine the effect of increased ruralInterstate speed limits on vehicle travel speeds (Esterlitz et al, 1989; Freedman andEsterlitz, 1990). One focus of these studies was the effects of uniform speed limits (e.g., 65mph for both trucks and passenger vehicles) versus the effects of differential speed limits(i.e., 55 mph for trucks, 65 mph for passenger vehicles).

Table 2-5 presents IIHS statistics (Esterlitz et al, 1989) taken in 1988 from four states: twouniform 65/65 (Arizona and Iowa) and two differential truck 55/PV 65 (Illinois and

California). Travel speeds were recorded from in-pavement induction loops or loop mats;all vehicles greater than 20 feet in length were classified as trucks. Thus, this categoryincludes single-unit trucks, buses, and other large vehicles. In all there were approximately60,000 vehicle observations. Truck highway travel speed averaged less than the speed limitin 65 mph states, but greater than the speed limit in 55 mph states. In all four states,trucks had lower average travel speeds and a smaller percentage of vehicles exceeding 70mph. Not surprisingly, this difference was greatest for the two states with differential speedlimits for cars and trucks.

Table 2-6 contains data collected by IIHS (Freedman and Esterlitz, 1990) in .Iune, 1989 inthree states: New Mexico (uniform 65/65), Virginia (differential 55 trucks, 65 passenger

vehicles), and Maryland (uniform 55). Speeds were recorded using a nondetectable K-bandradar, and vehicle types were recorded by observers. In this study, all trucks were tractor-trailers. The study results, representing a total of approximately 5,500 vehicle observations,corroborate those shown in Table 2-5. Moreover, data collected at the same sites in 1988and earlier in 1989 as part of the same study yielded similar results.

Also apparent in the Freedman and Esterlitz (1990) data is the fact that the percentage of speeding trucks decreases, relative to passenger cars, at higher travel speeds. Thus, in the

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2. Travel Speed Statistic

Maryland data, one sees that the percentage of trucks traveling at >65 mph is 80 percent of the passenger vehicle percentage, but that the percentage of trucks traveling at >70 mph is

only 37 percent of the passenger vehicle percentage.

TABLE 2-5: TRUCK AND PASSENGER VEHICLE MEAN TRAVEL SPEEDS AT 12 SITES IN4 STATES. (Esterlitz et al, 1989)

TABLE 2-6: PERCENT OF TRUCKS AND PASSENGER VEHICLES EXCEEDING 65 MPH AND70 MPH AT 11 SITES IN 3 STATES. (Freedman and Esterlitz, 1990; data shown collected inJune, 1989)

State # Sites SL Avg TS % > 65

4

VA 1 5

MD 2 Trk: 55 Trk: 61.1 Trk: 22.3%PV: 55 PV: 61 .6 PV: 2 7 . 8 %

Trk: 14.0%PV: 23.6%

Trk: 5.1%PV: 25.2%

Trk: 2.3%PV: 6.3%

IIHS (Status Report, February 3, 1990) cited additional data from nine northeastern statesrelating to compliance with 55 and 65 mph speed limits on Interstates. Table 2-7 presentsthese statistics. In all states except Vermont, the percentage of trucks exceeding 70 mphwas less than that of passenger vehicles. The difference in the percentage of vehiclesexceeding 70 mph was greatest in the five states with uniform 55 mph speed limits and inOhio, which has a differential (55 truck/65 passenger vehicle) speed limit. Two of thethree states with uniform 65 mph speed limits showed significantly smaller percentages of trucks than passenger vehicles exceeding 70 mph.

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TABLE 2-6: PERCENT OF TRUCK AND PASSENGER VEHICLES TRAVELING AT SPEEDSEXCEEDING 70 MPH IN 9 NORTHEASTERN STATES. (IIHS, 1990)

State

CT

I PA

I % > 70 II State

Trk:PV:

55 Trk:55 PV:

1% OH14%

Trk:PV:

5 5 Trk:55 PV:

Trk:PV:

5.5 Trk:55 PV:

3% VT9%

Trk:PV:

55 Trk :55 PV:

1% WV8% II

Trk:PV:

55 Trk :55 PV:

Trk:PV:

5565

Trk:PV:

Trk:PV:

6565

6565

Trk:PV:

6565

% > 70

Trk:PV:

Trk:PV:

Trk:PV:

4%27%

15%32%

25%23%

Trk:PV:

10%19%

2.3 Motor Carrier Safety Survey

Beilock (1989) conducted 1,285 interviews with long-haul truck drivers of tractor trailers fromCanada and the United States. This survey, conducted in conjunction with the RegularCommon Carrier Conference, addressed two principal issues relevant to the current study:

l Highway cruising speeds (perceived speeds of commercial trucks; not necessarilythe average cruising speed of the respondent)

. Acceptance and use of monitoring devices such as onboard computers, tachographs,and radar detectors (addressed in Chapter 4).

Interviewed drivers reported the perception that the 65 mph speed limit was exceeded by trucksless frequently than was the 55 mph speed limit. The average estimated cruising speed of commercial trucks (as perceived by drivers) was 60 mph on 55 mph highways and 67 mph on65 mph highways. These averages were nearly identical to those reported in 1988.

These survey results are based on drivers perceptions of the prevailing speeds of commercialtrucks, not on actual measurements. Obviously, these results should be interpreted withcaution. However, the RCCC survey results are generally consistent with the observationalstudies of truck speeds cited earlier in this chapter.

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3.0 STATISTICS ON HEAVY TRUCK SPEEDING-RELATED CRASHES

This chapter presents statistics relating to the question of how truck speeding contributes to theoverall truck crash picture. The emphasis is on crashes occurring at speeds in excess of 65 mphor 70 mph, since these would be the key targets of speed-limiting devices. Data have beenaccessed from four state accident databases and one national accident database, the FatalAccident Reporting System (FARS).These databases all differentiate combination-unit trucksfrom other vehicles, and contain the coded variables roadway posted speed limit (PSL) andvehicle travel speed (TS). These two variables, in combination, provide the basis forassessing the truck speeding issue, particularly the question of potential benefits from the use of devices that limit maximum vehicle speed. Another national database, the General EstimatesSystem (GES),has been used to provide baseline total national crash involvement estimates.

The data presented in this chapter represent vehicle involvements in police-reported trafficcrashes where the variables vehicle travel speed and posted speed limit were coded. Avehicle was considered to be speeding if its estimated travel speed exceeded the posted speedlimit. Estimated speeds are coded on Police Accident Reports (PAR S) by investigating policeofficers based on their post-crash investigations rather than direct observation of vehicle speed.Vehicle inspection, scene inspection, and interviews with drivers and witnesses are the keymethods for making this determination. Since there must be some clear indication of speedingbefore the officer will code it, the incidence of speeding is likely underreported in accidentdatabases. However, there is no known trend toward differentialunderreporting of speedinginvolvement for different vehicles types. Therefore, the assumption is made here that thesestatistics accurately portray relative speeding involvement for different vehicle types.

The PAR-reported travel speed statistics are probably more valid than other coded PARvariables thatmight be used to attempt to isolate speeding involvement in crashes. Forexample, the data attribute Violation: Speeding is likely to understate actual speeding evenmore seriously, since the investigating officer must have clearphysical or eyewitness evidencebefore the speeding violation is charged (and thus coded on the PAR). For example, in 1988-89combined, there were only nine FARS cases in which a fatal crash-involved combination-unittruck traveling on a 65 mph highway was charged with a speeding violation. There were only44 such cases for passenger vehicles. These counts likely understate actual high-speedinvolvement by a significant degree. Therefore, statistics on speeding violations are notconsidered to be valid indicators of actual speeding involvement.

Note also that all statistics reported in this chapter are based on counts of crash-involvedvehicles, as opposed to counts of crashes. Thus, a two-vehicle crash involving a truck and anontruckwould contribute one involvement in each category. Comparative statistics areprovided for combination-unit trucks, single-unit trucks, and passenger vehicles, although thelatter category here contains all motor vehicles other than combination-unit and single-unittrucks. Approximately 97 percent of the passenger vehicle category consists of automobilesand light trucks/vans, with the remainder being motorcycles, buses, and other miscellaneousvehicles.


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3. Statistics on Speeding-Related Crashe

The most important caveat relating to all of the speeding-related crash statistics cited in thischapter is that the categorization speeding-related or high-speed related does notnecessarily assure that speeding was the primary cause of the crash. Virtually all crashes

involve multiple contributing factors. The elimination of any one factor may or may notprevent the crash. High-speed crashes typically involve some other driver error (e.g., followingtoo closely, improper lane change) that precipitates the crash. Eliminating the high-speedelement may, or may not, prevent the crash. Thus, the speeding-related and high-speed-relatedcrashes identified in this chapter should actually be viewed as potentialtarget crashes for speedcontrol devices. The actual effectiveness of such devices in preventing and/or reducing theseverity of these potential target crashes is unknown.

3.1 Selected State Statistics

This section presents state data based on police-reported crashes for four selected states:Florida, Georgia, Ohio, and Virginia. All of these code the crash variables vehicle travelspeedand posted speed limit. The speeding involvement statistics quoted for these statesshould be interpreted with caution. In addition to the general underreporting factor describedabove, missing data rates are generally high for the vehicle travel speed variable. In the fourstate files examined, the missing data rates for combination-unit trucks varied from 5 percent inVirginia to 29 percent in Georgia. Passenger vehicle missing data rates for travel speed werehigher in all four of these states, suggesting possible differential accuracy of the coding forcombination-unit trucks versus passenger vehicles. However, the direction or significance of the differential accuracy (if any) is not known.

The statistics for all four states are for time periods after speed limits were raised to 65 mph onrural Interstates. Two of the states (Florida and Georgia) implemented the rural Interstate65 mph speed limit uniformly for all vehicles including trucks. Ohio and Virginia implementeddifferential speed limits on rural Interstates. Thus, only Florida and Georgia can be used for adirect comparison between trucks and nontrucks at a PSL of 65 mph.

This chapter presents a summary of the state statistics, aggregated across states by maximumspeed limit for trucks. Statistics for Florida and Georgia are aggregated, since, as noted above,both of these states have 65 mph speed limits for all vehicles on rural Interstates. Statistics forOhio and Virginia are similarly aggregated, since these two states use the same differentialspeed limit system for trucks and passenger vehicles. The statistics shown in this section are

also aggregated across PSLs from 35 mph to 65 mph in order to capture high-speed driving onall roadways where it is likely to occur. Vehicles for which TS or PSL were coded asmissing or unknown are not included in the present statistics.

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3. Statistics on Speeding-Related Crash

3.1.1 States With 65 mph Maximum Speed Limits for Trucks and Passenger Vehicles(Florida and Georgia)

Table 3-1 presents travel speed statistics for crash-involved vehicles from two states (Floridaand Georgia) with 65 mph maximum speed limits for trucks and passenger vehicles. TheFlorida statistics are for the time period April 27 to December 31, 1987. The Georgia statisticsare for the time period February 19 to December 31, 1988. The percentages shown areunweighted means of the two states. The percentage of vehicles for four levels of speeding arepresented (note: > symbol used for greater than): speeding (TS > PSL), speeding > 65 mph,speeding > 70 mph, and speeding > 75 mph. Note that these categories of speeding are notmutually exclusive; e.g., the speeding category includes all vehicle travel speeds above theposted speed limit. The statistics relating to vehicles exceeding 70 mph are perhaps mostrelevant to the issue of mandated speed-limiting devices, since speed-limiting devices might beset at a value near 70 mph. Note also that on-grade crashes are included in the present state

percentages, since not all of the state files accessed included roadway profile as a variable.Table 3-1 shows that crash-involved passenger vehicles have the highest speeding percentages atall levels. In general, single-unit trucks have the lowest percentages for speedinvolvement.Note also that the combination-unit truck speeding percentage decreases at higher speeds, notonly in terms of absolute percentage, but also in relation to the passenger vehicle percentage.

Table 3- l: TS vs. PSL for Three Vehicle Types, Florida + Georgia. Comparison of estimated vehicle travelspeeds with posted speed limits for combination-unit trucks, single-unit trucks, and passenger vehiclesinvolved in crashes. All percentages are unweighted means of the two state samples.

Number of Crash-Involved

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3.1.2 States With Differential Maximum Speed Liiits for Trucks and Passenger Vehicles(Ohio and Virginia)

Table 3-2 presents travel speed statistics for crash-involved vehicles from two states (Ohio andVirginia) with differential maximum speed limits for trucks (55 mph) and passenger vehicles(65 mph). The Ohio statistics are from the time period January 1 to September 30, 1988. TheVirginia statistics are for the time period July 1 to December 31, 1988. The percentages shown.are unweighted means of the two states, except that only Virginia statistics are used for the>70 mph category, since Ohio does not code travel speeds to this level of detail. The data inTable 3-2 are arrayed as in Table 3-1.

Crash-involved single-unit trucks have lower percentages of all levels of speeding involvementthan do the other vehicle types. Crash-involved combination trucks have a slightly higherspeeding percentage (5.60 percent) than do passenger vehicles (4.92 percent). However, the

percentages of crash-involved vehicles exceeding 65 mph, 70 mph, and 75 mph are lower forcombination trucks than for passenger vehicles.

Recall from Chapter 2 (e.g., Tables 2-2, 2-3, 2-5, 2-6 ) that trucks are more likely to exceed thespeed limit on 55 mph highways than on 65 mph highways, particularly when passengervehicles are permitted to travel at 65 mph. The finding that a larger percentage of accident-involved combination trucks than passenger vehicles in Ohio and Virginia were speeding isconsistent with the Chapter 2 findings.

Table 3-2: TS vs. PSE for Three Vehicle Types, Ohio + Virginia. Comparison of estimated vehicle travelspeeds with posted speed limits for combination-unit trucks, single-unit trucks, and passenger vehiclesinvolved in crashes. All percentages are unweighted means of the two state samples.

VA: 85 001

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3.2 Fatal Accident Reporting System (FARS) Statistics

.

The Fatal Accident Reporting System (FARS)is a national census of all fatal traffic crashes.

FARS is based primarily on PAR data. Like the four state databases in Section 3.1, FARSincludes the variables of vehicle travel speed (TS) and posted speed limit (PSL). The FARSstatistics presented here (Table 3-3) are limited to those 1988 and 89 fatal crash involvementsfor which both TS and PSL were known. This represents 42 percent of the FARS cases forthese two years. To isolate target crashes, the FARS Roadway Profile variable was used toeliminate on-grade crashes occurring at speeds greater than 65 mph. This is based on thepresumption that such high speed crashes occurring on a grade were likely downhill crasheswhere speed-limiting devices would not likely have affected vehicle speed.

Both fatal-accident-involved combination-unit trucks and single-unit trucks have considerablylower speeding percentages than do passenger vehicles in all four categories: speeding,

speeding > 65 mph, speeding > 70 mph, and speeding > 75 mph. Section 3.3 (below) presentsannual fatal crash involvement national problem estimates based on these statistics regardingtarget crash involvements at various travel speeds.

Table 3-3: TS vs. PSL for Three Vehicle Types Involved in Fatal Crashes. Percentage of fatal crashinvolvements (with TS and PSL known) involving speeding at various levels for combination-unittrucks, single-unit trucks, and passenger vehicles (raw counts, 1988-89 two-year total, FARS).Percentages for > 65 mph, > 70 mph, and > 75 mph crash involvements are based on not-on-gradecrashes only.

& PSL Known)

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3.3 Problem Size Estimates: Speed-Monitoring and Speed-LimitingTarget Crash Involvements

This section presents problem size estimates for the target crashes of speed monitoringand speed-limiting devices. The statistics on speeding-related crashes presented in Sections.3.1 and 3.2 can be used to estimate the number of speed-monitoring device and speed-limiting device target crashes, and to derive target crash involvement rates (i.e.,involvements per 100 million vehicle miles traveled) and likelihoods (i.e., number of annualinvolvements per 1,000 vehicles). These statistics provide additional insights into the extentof involvement of combination-unit trucks (and other vehicles) in speeding-related crashes.Three levels of speeding are assessed: all speeding (TS > PSL), speeding in excess of 65mph, and speeding in excess of 70 mph. Speed-monitoring devices could potentially beused as a countermeasure against all of these categories (if the posted speed limits of theroadways traveled were known), whereas speed-limiting devices would only target crashesabove their maximum speed set point (e.g., 70 mph).

Section 3.3.1 addresses speeding-related crashes (TS >PSL). Section 3.3.2 addresses crashesinvolving travel speeds exceeding 65 mph, the national maximum legal speed. Section 3.3.3addresses crashes involving travel speeds greater than 70 mph. Speed-limiting devices, if mandated, might be set at some value slightly higher than 65 mph to permit some tolerancefor additional power needed for hill-climbing or passing. Thus the selection here of 70 mphas a travel speed value for analysis.

3.3.1 Problem Size Estimates: Speeding-Related Crashes

Speeding-related crashes (i.e., speeding at any posted speed limit) might represent thosetargeted by the use of speed monitoring devices, with the caveat that the applicability of speed monitors to crashes at posted speed limits of less than 55 mph is questionable.Measures of problem size include involvement rate (i.e., involvements per 100 millionvehicle miles traveled) and number of annual involvements per 1,000 vehicles. The analysisis based on police-reported speed involvement in crashes, supplemented by statistics onvehicle miles traveled (VMT) and vehicle registration counts.

Tables 3-4 and 3-5 present these statistics for three vehicle types (combination-unit trucks,single-unit trucks, and passenger vehicles) for speeding-related crashes. The tables are

based on 1988-89 GES and FARS, annual VMT estimates (FHWA), and vehicleregistrations (FHWA). Table 3-4 presents the statistics for all crashes (using average 1988-89 GES crash estimates). The percentages used for speeding-related vehicle involvementsin crashes are the unweighted mean of the four states reported here (Florida, Georgia,Ohio, and Virginia). Table 3-5 presents statistics for fatal crashes, based on 1988-89 FARSdata. As was noted in Section 3.1, speeding is thought to be underreported on PARS,although there is no known trend toward differentialunderreporting of speeding of differentvehicle types. Therefore, the assumption is made here that the statistics presented in

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3. Statistics on Speeding-Related Crash

Tables 3-4 and 3-5 are generally accurate in terms of the relative involvements of differentvehicle types.

The data on speeding-related crashes indicate that, by all measures, single-unit trucks aresignificantly underinvolved in speeding-related crashes relative to other vehicle types. Thisis true both for all speeding-related crashes (Table 3-A) and fatal crashes (Table 3-5). Ascompared to passenger vehicles, combination-unit trucks have lower percentages of crashinvolvements and fatal crash involvements where speeding is indicated, and far lower ratesof speeding-related crashes per 100 million vehicle miles traveled (VMT). However, theirannual likelihoods of involvement (per 1,000 vehicles) in speeding-related crashes and fatalcrashes are greater for combination-unit trucks than for other vehicle types due to theirhigh exposure (annual mileage per vehicle).

The absolute size of the truck speeding-related crash problem is small in relation to that of

all vehicle types combined. The combined number of speeding-related crash involvementsfor combination-unit trucks and single-unit trucks (14,300) is only about 2 percent of thetotal for all vehicle types (approximately 652,000).

Table 3-4: Problem Size Estimates: Speeding-Related Crashes for Three Vehicle Types Based on Indicationsof Speeding on PARs.


Annual Vehicle Involvements in Crashes (1988- 2 2 0 , 0 0 0 1 2 2 , 0 0 0 11,440,000$9 Average, GES)

Percent Speeding-Related 5.03% 3.05% 5.57%(Unweighted Mean: FL, GA, VA, & OH)

Estimated Annual Number Speeding-Related 10,200 4,100 638,000Vehicle Involvements in Crashes

Annual VMT (Millions; FIIWA)

Involvement Rate, Speeding-Related Crashes(Per 100 M VMT)

90,149 51,231 1,884,207

11.3 7.9 33.8

Vehicle Registrations (FI-IWA)

Annual Number Speeding-Related CrashInvolvements Per 1,000 Vehicles

1,476,241 3,957,319 183,547,456

6.9 1.0 3.5

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Table 3-5: Problem Size Estimates: Fatal Speeding-Related Crashes for Three Vehicle Types Based onIndications of Speeding on PARs

Statistic Vehicle Type: Comb-Unit Trks

Annual VMT (Millions; FHWA)

Involvement Rate, Speeding-Related FatalCrashes (Per 100 M VMT)

90,149 51,231 1,884,207

0.0058 0.0013 0.0094

Vehicle Registrations (FHWA)

Annual Number Speeding-Related Fatal CrashInvolvements Per 1,000 Vehicles

1,476,241 3,957,319 183,547,456

0.35 0.02 0.10


This section estimates the problem sizes of crashes involving police-reported speeds of greaterthan 65 mph, the national maximum speed limit. Crashes occurring at speeds in excess of

65 mph could be potential target crashes of both speed-monitoring and speed-limiting devices.The statistics derived are analogous to those derived in Section 3.3.1 above, except that onlynon-grade crashes are included in the target crash estimates. This reflects the fact that speed-limiting devices would have little effect on downgrade crashes occurring at speeds greater than65 mph, since most such truck crashes would involve a free-roll situation where road speedgovernors would not affect vehicle speed.

Tables 3-6 presents > 65 mph crash problem size estimates based on national crash involvementestimates (1988-89 GES) and percentage speeding > 65 mph based on two states that recordvehicle travel speed, Florida and Georgia. Both Florida and Georgia have uniform 65/65 speedlimits on rural Interstates for trucks and cars (as do most states nationally). Using two states

with uniform 65/65rural Interstate speed limits for this analysis helps ensure comparabilitybetween vehicle types. To eliminate crashes occurring on downgrades from the problem sizeestimates, the GES total crash estimates were first modified to omit crash involvementsoccurring on grades.

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Table 3-6: Problem Size Estimates: Speeding > 65 mph-Related Not-on-Grade Crashes for Three VehicleTypes Based on Indications of Speeding on PARs.


Annual Vehicle Involvements in Crashes 220,000 122,000 11,440,000(1988-89 GES)

Annual Crash Involvements, Not on Grade(1988-89 GES)

179,000 98,000 9,731,000

Percent Speeding > 65 mph-Related(Unweighted Mean: FL, GA)

Estimated Annual Number Speeding > 65mph-Related Vehicle Involvements in Crashes

0.51% 0.21% 0.89%

910 200 86,600

Annual VMT (Millions; FIIWA) 90,149 51 ,231 1,884,207

Involvement Rate, Speeding > 65 mph-RelatedCrashes (Per 100 M VMT)

1.01 0.40 4.60

Vehicle Registrations (FIIWA) 1,476,241 3,957,319 183,547,456

Annual Likelihood; Speeding > 65 mph-Related Crash Involvements Per 1,000Vehicles

0.62 0.05 0.47

Table 3-7: Problem Size Estimates: Fatal Speeding > 65 mph-Related Not-on-Grade Crashes for ThreeVehicle Types Based on Indications of Speeding on PARs

Statistic Vehicle Tvoe: Comb-Unit Trks Sngl-Unit Trks Pass. Vehs.

Annual Vehicle Involvements in Fatal Crashes(1988-89 FARS)

4,063 1,051 56,612

Percent Speeding > 65 mph-Related 1.7% I 1.0% | 9.6%Est. Ann. Number Speeding > 65 mph-Related 69 10 5,414Fatal Crash Involvements (& Fatalities) (73) (12) (5,795)

Annual VMT (Millions; FIIWA)

Involvement Rate, Speeding > 65 mph-RelatedFatal Crashes (Per 100 M VMT)

Vehicle Registrations (FHWA)

Annual Likelihood; Speeding > 65 mph-Related Fatal Crash Involvements Per 1,000Vehicles

90,149 51 ,231 1,884,207I

0.08 0 .02 0.29

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3. Statisticson Speeding-Relat ed Crashes

Table 3-7 presents speeding > 65 mph fatal crash involvement problem size estimates based on1988-89 FARS statistics. FARS cases with unknown TS and/or PSL values were distributedproportionately to those with known values in order to generate national estimates of speeding > 65 mph-related fatal crash involvements.

The statistics on speeding > 65 mph crashes and fatal crashes indicate that, as for speeding-related crashes, single-unit trucks have the lowest levels of involvement regardless of thestatistical metric used. Combination-unit trucks have lower percentages and rates of crashinvolvements and fatal crash involvements where speeding > 65 mph is indicated than dopassenger vehicles. However, as previously, their annual likelihoods of involvement (per1,000 vehicles) in speeding > 65 mph-related crashes a

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